Fungal Infection Testing in Pediatric Intensive Care Units—A Single Center Experience

Mycoses are diseases caused by fungi that involve different parts of the body and can generate dangerous treatment complications. This study aims to analyze fungal infection epidemiology in intensive care units (Pediatric and Cardiac Surgery Intensive Care Units—PCICU) and the Neonatal Intensive Care Unit (NICU) in one large pediatric center in the period 2015–2020 compared with 2005. The year 2005 was randomly selected as a historical time reference to notice possible changes. In 2005 and 2015–2020, 23,334 mycological tests were performed in intensive care units. A total of 4628 tests (19.8%) were performed in the intensive care units. Microbiological diagnostics involved mycological and serological testing. Of the 458 children hospitalized in the NICU, positive results in the mycological tests in the studied years were found in 21–27% of the children and out of 1056 PCICU patients, positive results were noticed in 18–29%. In both departments, the main detected pathogen was Candida albicans which is comparable with data published in other centers. Our experience indicates that blood cultures as well as the detection of antifungal antibodies do not add important information to mycological diagnostics. For the years of observation, only a few positive results were detected, even in patients with invasive fungal diseases. To our knowledge, this is one of a few similar studies over recent years and it provides contemporary reports of mycoses in pediatric ICU patients.


Introduction
Mycoses or fungal diseases can be divided into superficial, subcutaneous, and systemic. Invasive fungal infection (IFI) is a severe, systemic, life-threatening disease caused by fungi [1]. IFIs are a leading cause of morbidity and mortality in immunocompromised children and neonates [2]. However, even the common fungal infection could be dangerous for a severely ill child as it leads to an inflammatory reaction, an additional therapy risk, or a delay in treatment.
The majority of our knowledge comes from adult population or pediatric cancer patient single center studies [3,4]. Nonspecific symptoms, diagnostic challenges, and the occasional usage of anti-fungal prophylaxis could be the reasons why many cases of fungal infections remain undiagnosed. According to the revised criteria of the EORTC/MSG Consensus Group, adequate microbiological evaluation is the key to the accurate diagnosis of fungal infections ensuring appropriate treatment [5]. 2 of 15 The study was conducted in a tertiary care pediatric referral center in southern Poland that is comprised of 24 departments including 3 pediatric intensive care units and a separate neonatal intensive care unit. The hospital has 33,000 admissions per year and performs approximately 7000 operations including 450 cardiac surgery procedures per year on average. In the intensive care units, children with the most advanced forms of various congenital defects and burns, or neonates with extremely low birth weights are managed. Moreover, intensive therapy departments provide care for patients after complex surgeries (including cardiac and brain procedures), after accidents, or with severe complications after multimodal oncological treatment. Therefore, children treated in these units are at a high risk of hospital-acquired infections as some of them are immunocompromised or malnourished, or are undergoing combined antibiotic therapy which makes them a population extremely prone to fungal infections.
The hospital provides comprehensive diagnostic services for every patient with a suspected fungal infection. Various radiological imaging methods help patients with advanced mycoses to be recognized. Surgical procedures are often necessary to obtain the appropriate material. In the Microbiology Department, various diagnostic methods are routinely ordered including fungal cultures on samples from several body regions. Moreover, detailed serological tests are used to expand the patient's evaluation.
The aim of the study was to analyze the epidemiology of fungal infections in the intensive care units (Pediatric and Cardiac Surgery Intensive Care Units-PCICU) and the Neonatal Intensive Care Unit (NICU) of the Children's University Hospital (UCH) in Krakow in the period 2015-2020. The data were compared with previous data collected in 2005 to notice possible changes.

Materials and Methods
In 2005 and 2015-2020, the Clinical Microbiology Department of UCH performed a total of 23,334 mycological tests. A total of 4628 tests (19.8%) were performed in the intensive care units, including 3755 tests for (PCICU) and 873 for NICU. The year 2005 was used as a baseline to estimate changes in the amount of performed tests and cultured fungi.
For the statistical analysis of the collected data, we used Statistica 13 (StatSoft, INC., Tulsa, OK, USA). The incidence of positive results for each year was compared using Pearson's chi-squared test.
The distribution of the results collected from PCICU in the studied years, including the number of positive tests is shown in Figure 2.
During the studied period, 205 out of 873 mycological tests collected from the NICU were positive. Figure     During the studied period, 205 out of 873 mycological tests collected from the NICU were positive. Figure 3 shows the number of collected samples each year divided into five source groups: (1) gastrointestinal track-332 tests, (2) upper respiratory tract-15 tests,             No statistically significant differences between the positive and negative results were found. The most frequently isolated species in the gastrointestinal tract NICU samples can be found in Figure 10.  Table 3.
Upper respiratory tract samples from NICU patients were collected from 14 patients (15 probes in total). Four yeast isolates were found. More details are presented in Table 4. The prevalence of positive results in the studied years was as follows: 2005-0%, 2015-100% (2/2), 2016-17% (1/6), 2017-0%, 2018-100% (1/1), 2019-0%, and 2020-0%. No statistically significant differences between the positive and negative results were found. Lower respiratory tract samples from PCICU patients were collected from 668 patients (1396 probes in total). A total of 259 yeast isolates were found. More details are shown in Table 5. Lower respiratory tract samples from NICU patients were collected in 141 patients (193 probes in total). A total of 27 yeast isolates were found. More details are shown in Table 6.
Urinary tract samples were collected in the group of 365 PCICU patients (587 probes in total) with 113 yeast isolates detected. More details can be found in Table 7

Year
Positive Results   The results of the study of antibody levels and the presence of positive fungal antigens (Aspergillus and Candida) in NICU patients can be found in Tables 13-16.   Table 13. Galactomannan Aspergillus antigen in NICU patients.

Year
Positive Results

Discussion
The study group was comprised of two subgroups of children treated in Intensive Care Units. Pediatric and Cardio Surgery Intensive Care Units (PCICU) patients are referred to the units due to complications from other hospital departments and after cardio surgical procedures. The primary reason for infections was severe conditions due to cardiac and respiratory disorders, multiorgan dysfunction, prolonged immobilization, secondary immunodeficiency, or the repeated cannulation of vessels. The Neonatal Intensive Care Unit (NICU) group is composed of premature babies and newborns with an increased risk of infections due to humoral immunodeficiency (decreased IgA, IgG, and IgM), decreased chemotaxis, low bone marrow reserve, decreased bowel movements, low acid concentration in the stomach, increased skin pH and permeability, as well as a lack of a proper composition of the microbiome [7]. The secondary factors that predispose patients to an increased rate of infections in those treated in all intensive care units were exposition to highly resistant pathogens due to colonization with hospital environment pathogens as well as the use of invasive diagnostics procedures and others such as mechanical ventilation, cannulation of large vessels, catheterization of the pulmonary artery and the urinary bladder, and intravenous alimentation. Together with prolonged hospitalization and repeated wide spectrum antibiotic therapy, the risk of fungal infection increases. In the 458 children presented (232 boys and 226 girls) that were hospitalized in NICU, positive results from the mycological tests in the studied years were found in 21-27% of the children. The main detected pathogen was Candida albicans which is comparable with data published in other centers [6][7][8][9]. Due to the common use of fluconazole in empiric antifungal prophylaxis in high-risk premature infants, an increased colonization of the gastrointestinal tract with Candida non-albicans was observed. The main pathogens were Candida parapsilosis (increase in all the studied years except 2017) and Candida glabrata in 2019 and 2020, which is in accordance with data published in the literature [8][9][10][11][12][13].
Our experience indicates that blood cultures do not add important information to mycological diagnostics. For the years of observation, only a few positive results were detected even in patients with invasive fungal diseases.
The same was true in relation to the detection of antifungal antibodies. Our results showed that such detection was very rare, even though those patients were not immunocompromised. If detected, the increased level of antibodies could suggest the status of fungal infection. In all units in the analyzed period, we detected anti-Aspergillus antibodies in only one patient and anti-Candida in four patients. Detection of the fungal antigen can be more informative. In our patients, such detection was more common compared to antibodies. It should be treated as a screening, as the diagnostics of fungal infection are very difficult. It would be useful to establish validated methods of detection for fungal antigens in urine, fluid from respiratory airways, and stools. Unfortunately, colonization with fungal pathogens, especially Candida albicans is common, which makes the detection of its antigen less useful, but the methodology of the testing should be adapted to that.
The majority of the studies on fungal infections have concentrated on oncology departments. The problem of mycoses in intensive care units is underdiagnosed. This study showed the necessity of screening for fungal diseases in these high-risk patients. Moreover, we concluded that the diagnostic methods are limited. There is an urgent need to introduce new validated mycological tests in order to improve the survival of children with the most advanced medical conditions. The International Pediatric Fungal Network ((PFN) www.ipfn.org accessed on 21 October 2021) was created to facilitate international cooperation in terms of the understanding and management of pediatric fungal infections.
Our study has some limitations characteristic of most retrospective data analyses. We focused on microbiological tests results and did not include the clinical characteristics of the patients. The data came from only one large center and therefore the results could reflect patterns specific for this center. However, the results from multicenter studies that we referred to are comparable to ours. Moreover, we avoided selection bias as we enrolled all patients treated in the ICUs with suspicion of a fungal infection in the study. To our knowledge, only a few similar studies have been published recently and our study provides a contemporary report of mycoses in pediatric intensive care patients.

Conclusions
Our experience, based on our center, indicates that the percentage of positive mycological tests in pediatric and neonatal intensive care units reached 18-29%. In both departments, the main detected pathogen was Candida albicans which is comparable with data published in other centers [14][15][16][17]. Our experience indicates that blood cultures as well as the detection of antifungal antibodies do not add important information to mycological diagnostics. For the years of observation, only a few positive results were detected, even in patients with invasive fungal diseases.